1. Field of the Invention
The present invention relates to a method of manufacturing a gate electrode which utilizes a refractory metal, or a wire which employs a refractory metal.
2. Description of the Related Art
A polycrystalline silicon gate electrode or a polycide gate electrode structure in which a tungsten silicide film is stacked on a polycrystalline silicon film, has heretofore generally been used as a structure of a gate electrode for a device. With a view toward implementing high integration and speeding-up of the device, the gate electrode stands in need of a further reduction in resistance, and the development of a technique for implementing it has been pursued.
As an example, a gate structure (Reference: Y. Akasaka et al., IEEE Trans. Electron Devices, ED-43, 1864 (1996)) called xe2x80x9cpolymetal gatexe2x80x9d has been reported in which a refractory metal such as tungsten, a barrier layer comprised of its nitride, and a polycrystalline silicon film are stacked on one another. This is considered to be a structure effective in implementing a low-resistance gate.
With high integration of the device, allowance for alignment of each contact hole to the source and drain with its corresponding gate electrode approaches the limit of the lithography technology. There has been an increasingly demand for application of a Self Aligned Contact (hereinafter called xe2x80x9cSACxe2x80x9d) technology in order to overcome such a limit.
The SAC technology is used with the objective of, when a portion above each gate electrode and side walls thereof are formed of silicon nitride films and contact holes reaching source and drain diffused layers are defined in an interlayer dielectric, the gate electrode is masked by these silicon nitride films, whereby the contact holes for the source and drain are formed on a self-alignment basis.
Forming a nitride film over a patterned polymetal gate and subjecting it to anisotropic etching forms side walls of a silicon nitride film. The nitride film is normally formed by a reduced pressure CVD method. The growth of the silicon nitride film by the reduced pressure CVD method is normally performed at a high temperature of 700xc2x0 C. or higher.
When the tungsten is used for a polymetal gate electrode, a tungsten oxide film is formed over exposed sides of the tungsten. When a wafer is subjected to a high temperature in a state in which such a tungsten oxide film has been formed, whisker is produced.
A reduction in the oxidization of the tungsten film upon deposition of the nitride film is important to inhibit the occurrence of the whisker. Therefore, there has been proposed a method of reducing a wafer insertion temperature from 550xc2x0 C. to 350xc2x0 C. or performing a reducing process using ammonia to remove oxygen in the tungsten oxide film formed over the tungsten film, for example. However, when the wafer insertion temperature is lowered, an increase in processing time takes place as a problem. Since the execution of the ammonia reducing process depends on processing pressure, it is difficult to set the optimum processing condition.
An object of the present invention is to provide a method of inhibiting the occurrence of whisker more reliably.
According to one aspect of the present invention, for achieving this object, a refractory metal film is formed over a semiconductor substrate and a first nitride film is formed over the refractory metal film. Thereafter, the refractory metal film and the nitride film are patterned and the sides of the patterned refractory metal film are nitrided.